The present invention relates to a roller support device in a molten metal plating bath which is assembled into a plating apparatus, which performs successive plating treatments of different metals such as molten zinc and the like on the surface of a metal plate such as a long steel plate or the like, to rotatably support a roller for guiding the metal plate.
When a metal is plated on the surface thereof with a layer of a second metal, a plating method using an electrochemical treatment is used, a plating method using a so-called molten plating bath in which a metal serving as a core member is immersed in a plating bath in which the second metal is molten, is used. When a metal of a different kind such as zinc or the like is plated on the surface of a metal plate such as a long steel plate or the like by use of the above-mentioned molten plating bath, for example, as shown in Unexamined Japanese Utility Model Publication No. Sho. 61-90852 or Unexamined Japanese Patent Publication No. Hei. 5-187445, an apparatus as shown in FIGS. 4 and 5 is used.
A long metal plate 1 such as a steel plate or the like serving as a core member, which is fed out from an uncoiler (not shown), is guided by a suitable delivery roller 2 to pass through a continuous furnace 3 and a snout 4 and is further introduced into a plating vessel 6 in which a molten metal is stored. Then, the metal plate 1 is turned upwardly by a sink roller 7 and is fed through the plating vessel 6, whereby the molten metal 5 to serve as a plated layer is adhered to the surface of the metal plate 1. Then, a warp in the metal plate 1 is corrected by support rollers 8, 8 and thus the metal plate 1 is stabilized as a continuous plate, with the result that the metal plate 1 is taken out of the plating vessel 6 as a plated metal plate la. In FIG. 4, reference characters 9, 9 respectively designate nozzles which are used to regulate the amount of adhesion of the molten metal. After the plated metal plate 1a is passed through the nozzles 9, 9, the metal adhered to the surface of the plated metal plate 1a is cooled and solidified there, before the plated metal plate 1a is wound around a recoiler (not shown).
As described above, the sink roller 7 and support rollers 8, 8, respectively guide the metal plate 1 or rectifies the warp in the metal plate 1 while the metal plate 1 is immerse in the molten metal 5 at high temperatures. The respective ends of the sink roller 7 and support rollers 8, 8, for example, as shown in FIG. 5, are rotatably supported on the end portions of a pair of-support arms 10, 10 through rolling bearings 11, 11. That is, circular holes 12, 12 are respectively formed in the end portions of the support arms 10, 10. And, the above-mentioned rolling bearings 11, 11 are respectively interposed between the inner peripheral surfaces of the circular holes 12, 12 and the outer peripheral surfaces of shafts 13, 13 respectively projected out from the two end faces of the support roller 8, so that the support roller 8 is free to rotate. A support device for the sink roller 7 is structured in a similar manner.
Since the rolling bearings 11, 11 are required to have high thermal resistance, they may be formed of ceramics or the like. That is, the rolling bearings 11, 11 are respectively composed of outer races 14, inner races 15, and a plurality of rolling elements 16, 16, all of which are formed of ceramics such as silicon nitride (Si.sub.3 N.sub.4) or the like. Also, the plurality of rolling elements 16, 16 are rollingly supported by a cage 26 (e.g., as shown in FIGS. 1 and 2) in such a manner that mutually adjoining rolling elements 16, 16 are spaced a predetermined distance from each other.
In the above-mentioned manner, for example, the outer races 14, 14 that form a pair of rolling bearings 11, 11 for supporting the two end portions of the support roller 8 are respectively combined with alignment rings 17, 17 to form an outer race unit. That is, the respective outer races 14, 14 are pivotally fitted into the alignment rings 17, 17 to thereby form an automatic self-aligning bearing which is free to make up for misalignment between the axes of the outer races 14, 14 and the axes of the alignment rings 17, 17. And, the pair of alignment rings 17, 17 are supported in the insides of the circular holes 12, 12 through bearing boxes 18a, 18b, respectively. Further, one alignment ring (the right one in FIG. 5) of the pair of alignment rings 17, 17 is supported in the inside of the bearing box 18a for supporting the alignment ring 17 in such a manner that it cannot be shifted in the axial direction (in FIG. 5, in the right and left direction). On the other hand, the other alignment ring 17 (the left one in FIG. 5) is supported in the inside of the bearing box 18b for supporting the alignment ring 17 in such a manner that it can be freely shifted in the axial direction (in FIG. 5, in the right and left direction).
As described above, the reason why the other alignment ring 17 is supported in the inside of the circular hole 12 through the bearing box 18b in such a manner that it is free to shift in the axial direction is to absorb the thermal expansion and contraction of the support roller 8 due to changes in the temperature thereof. That is, while the plating apparatus is in use, the temperature of the support roller 8 rises up to a temperature of the order of 450.degree. C. which is equal to the temperature of the molten metal 5 within the plating vessel 6 and, on the other hand, when the support roller 8 is taken up from the plating vessel 6 for maintenance, inspection or other purposes, the temperature of the support roller 8 falls to a room temperature. In this manner, the whole length of the support roller 8 varies to a considerable extent in accordance with the thermal expansion and contraction thereof between the time while the plating apparatus is in use and the time for maintenance or inspection thereof. This requires means for absorbing the variation in the whole length of the support roller 8. For this reason, as described above, one alignment ring 17 is supported in the inside of the bearing box 18b in such a manner that it is free to shift in the axial direction, so that the variation in the whole length of the support roller can be absorbed freely.
If the support roller 8 immersed in the molten metal 5 is taken up from the plating vessel 6 for maintenance, inspection or other operations thereof, then the other alignment ring 17 shifts to the right in FIG. 5 as the length of the support roller 8 is contracted in accordance with drops in the temperature of the support roller 8, thereby being able to absorb the amount of the contraction.
However, in the above-mentioned conventional roller support device in a molten metal plating bath, there are still remaining problems, which will be described below. That is, if the support roller 8 immersed in the molten metal 5 is taken up and is exposed to the air for maintenance, inspection or other purposes, then it is inevitable that part of the molten metal adheres to the inner peripheral surface of the bearing box 18b. And, the molten metal adhered to the inner peripheral surface of the bearing box 18b will be cooled and solidified before the temperature of the support roller 8 falls down sufficiently and thus the whole length of the support roller 8 is contracted completely.
When the thus cooled and solidified metal remains adhered to the inner peripheral surface of the bearing box 18b, then the adhered zinc prevents the alignment ring 17 from shifting in the axial direction within the bearing box 18b. As a result of this, as the support roller 8 is contracted, excessive forces are applied to the pair of rolling bearings 11, 11 in the thrust direction thereof, so that the rolling bearings 11, 11 can be broken.
That is, when the roller support device is used in the molten metal for a long period of time, as described above, rollers such as the support roller 8 and the like and the bearing portions of the end portions of the rollers are taken out from the molten metal bath into the air. And, such immersion of the rollers into the molten metal bath and taking-out of the rollers form the molten metal bath are carried out repeatedly and the support roller 8 is expanded and contracted each time it is immersed into and taken out from the molten metal bath. For this reason, one rolling bearing 11 of the pair of rolling bearings 11, 11 for supporting the two ends of the support roller 8 is fixed (that is, it is set immovable in the axial direction) and, at the same time, the other rolling bearing 11 is supported in such a manner that it can shift in the axial direction.
However, if the molten metal adheres to the sliding portion of the other rolling bearing 11 and is further solidified, then the adhered and solidified molten metal prevents the other rolling bearing 11 from shifting in the axial direction and, with the expansion and contraction of the support roller 8, a great thrust force is applied to both rolling bearings 11. And, if the thrust force becomes excessive, then the pair of rolling bearings 11, 11 supporting the two ends of the support roller 8, alignment ring 17, bearing boxes 18a, 18b, or the support arms 10, 10 respectively supporting the rolling bearings can be broken.